Psittacosis is a zoonotic infection caused by Chlamydia psittaci, an obligate intracellular gram-negative bacterium that causes avian chlamydiosis in birds and systemic disease in humans [1][5]. It is classified among the most common atypical pneumonias, which are systemic infectious diseases with a pulmonary component that may be differentiated from typical community-acquired pneumonias by characteristic patterns of extrapulmonary organ involvement [5].
Disease overview
BacterialPsittacosis
鹦鹉热
Evidence-backed informationEN 5/7 applicable sections · ZH 5/7 applicable sectionsUpdated Sep 3, 2026
Chlamydia psittaci is an obligate intracellular gram-negative bacterium with a biphasic developmental cycle that causes avian chlamydiosis in birds and psittacosis in humans [1]. It is a zoonotic pathogen with a wide range of avian hosts, and human infection occurs primarily through exposure to infected birds [1][2]. Person-to-person transmission has been confirmed in the last decade, though bird contact remains the dominant route [1][3]. The disease manifests as an atypical pneumonia with systemic features, ranging from asymptomatic infection to severe disease [2][4].
Read the full clinical and epidemiological profile6
Psittacosis presents with a typical clinical picture of atypical pneumonia, including approximately one week of fever, headache, myalgias, and nonproductive cough [4]. Pneumonia is the most common manifestation, though all organ systems may be involved as these atypical agents often cause extrapulmonary manifestations [5][4]. The infection is associated with a spectrum of disease severity ranging from asymptomatic infection to severe atypical pneumonia and systemic disease [2].
Current disease surveys indicate that the highest incidences of human psittacosis exist in Australia, Germany, and the United Kingdom [3]. In Belgium, reported positive laboratory results increased slowly since 2010, nearly doubling in 2017 compared to the two previous years [2]. The number of psittacosis cases is probably highly underestimated in Belgium and other countries due to underdiagnosis and underreporting; the mandatory notification system captured only 24% of all reported positive laboratory results over a three-year period [2].
The primary transmission route is through exposure to infected birds, including both horizontal transmission between birds and cross-species transmission to humans [1]. Human-to-human transmission has recently been confirmed, though bird contact remains the dominant route [1][3]. The pathogen's wide range of avian hosts facilitates ongoing transmission to humans [1].
C. psittaci is primarily transmitted horizontally among birds, and although cross-species transmission to humans occurs, prevention is framed within a One Health approach that integrates avian chlamydiosis and human psittacosis [1]. A basic understanding of the pathogen's genotype, host–pathogen interactions, transmission, epidemiology, detection, and clinical management supports targeted control strategies across avian and human populations [1].
- 1Wang J et al. Chlamydia psittaci: A zoonotic pathogen causing avian chlamydiosis and psittacosis. Virulence. 2024 Dec. PMID: 39541409. doi: 10.1080/21505594.2024.2428411.PubMed: https://pubmed.ncbi.nlm.nih.gov/39541409/
- 2Rybarczyk J et al. Human psittacosis: a review with emphasis on surveillance in Belgium. Acta Clin Belg. 2020 Feb. PMID: 30882289. doi: 10.1080/17843286.2019.1590889.PubMed: https://pubmed.ncbi.nlm.nih.gov/30882289/
- 3Dembek ZF et al. Psittacosis: An Underappreciated and Often Undiagnosed Disease. Pathogens. 2023 Sep 15. PMID: 37764973. doi: 10.3390/pathogens12091165.PubMed: https://pubmed.ncbi.nlm.nih.gov/37764973/
- 4Stewardson AJ et al. Psittacosis. Infect Dis Clin North Am. 2010 Mar. PMID: 20171542. doi: 10.1016/j.idc.2009.10.003.PubMed: https://pubmed.ncbi.nlm.nih.gov/20171542/
- 5Cunha BA et al. The atypical pneumonias: clinical diagnosis and importance. Clin Microbiol Infect. 2006 May. PMID: 16669925. doi: 10.1111/j.1469-0691.2006.01393.x.PubMed: https://pubmed.ncbi.nlm.nih.gov/16669925/
Coverage
Reporting countries and regions
Trends by reporting country
Monthly patterns over time
Research Radar
Recent related research
Diagnosis and treatment experience of Chlamydia psittaci pneumonia: A multicenter retrospective study in China
BMC Infectious Diseases
Chlamydia psittaci (psittacosis) as a cause of community-acquired pneumonia: a systematic review and meta-analysis
Epidemiology and Infection
Literature links are provided for discovery and do not alter or validate the surveillance series above.
Data access
Page dataset index with source links and update metadata.
Official sourcesAuthority, cadence, notes19
Australia NINDSS
Australia
Australian national notifiable diseases surveillance dashboard.
Australia NINDSS — Australian Capital Territory
Australian Capital Territory, Australia
Australian NINDSS monthly state/territory notifications for Australian Capital Territory, kept separate from the Australia national aggregate.
Australia NINDSS — New South Wales
New South Wales, Australia
Australian NINDSS monthly state/territory notifications for New South Wales, kept separate from the Australia national aggregate.
Australia NINDSS — Northern Territory
Northern Territory, Australia
Australian NINDSS monthly state/territory notifications for Northern Territory, kept separate from the Australia national aggregate.
Australia NINDSS — Queensland
Queensland, Australia
Australian NINDSS monthly state/territory notifications for Queensland, kept separate from the Australia national aggregate.
Australia NINDSS — South Australia
South Australia, Australia
Australian NINDSS monthly state/territory notifications for South Australia, kept separate from the Australia national aggregate.
Australia NINDSS — Tasmania
Tasmania, Australia
Australian NINDSS monthly state/territory notifications for Tasmania, kept separate from the Australia national aggregate.
Australia NINDSS — Victoria
Victoria, Australia
Australian NINDSS monthly state/territory notifications for Victoria, kept separate from the Australia national aggregate.
Australia NINDSS — Western Australia
Western Australia, Australia
Australian NINDSS monthly state/territory notifications for Western Australia, kept separate from the Australia national aggregate.
Hong Kong, China CHP Notifiable Diseases
Hong Kong, China
Hong Kong, China CHP annual notifiable infectious disease CSVs normalized to national monthly totals
Iceland Directorate of Health Annual Dashboard
Iceland
National annual case notifications by disease. Published values can be revised retrospectively and remain annual period totals.
Iceland Directorate of Health STI Dashboard
Iceland
Monthly STI diagnosis facts from laboratory and registry surveillance; the official dashboard is published on a quarterly schedule.
Iceland Directorate of Health Respiratory Dashboard
Iceland
ISO-week respiratory diagnosis counts. Hospitalizations, samples, and vaccination indicators are separate measures and are not counted as diagnoses.
Iceland Directorate of Health Historical Registry
Iceland
Historical official registry tables for 1997–2021, with annual totals and disease-specific monthly notification facts retained at source grain.
Iceland Directorate of Health Legacy ICD Monthly
Iceland
Historical Saga EHR ICD encounter counts for 1997–2020. This clinical measure is non-comparable with registry notifications and is kept separate.
JP NIID Weekly
Japan
Japan weekly infectious disease surveillance via NIID/JIHS.
Sweden Public Health Agency SmiNet
Sweden
Sweden SmiNet national monthly reported cases from the official Public Health Agency statistics pages; public release is enabled with closed-month publication and revisable recent-month refreshes.
US CDC NNDSS
United States
CDC National Notifiable Diseases Surveillance System provisional data.
US CDC NHSS HIV
United States
CDC NNDSS weekly data plus NHSS annual national HIV diagnoses